Communication apparatus and method of detecting downlink control information

ABSTRACT

Disclosed is a transmission apparatus capable of properly performing cross carrier scheduling in ePDCCHs. In this apparatus, when communication is performed using a plurality of component carriers (CCs), configuration section  102  configures a first search space as a candidate to which control information for a first CC is assigned and a second search space as a candidate to which control information for a second CC other than the first CC among the plurality of CCs is assigned, within a same allocation unit group among a plurality of allocation unit groups included in a data-assignable region within the first CC, and transmission section  106  transmits control information mapped to the first search space and control information mapped to the second search space.

BACKGROUND Technical Field

The present disclosure relates to a transmission apparatus, a receptionapparatus, a transmission method, and a reception method.

Description of the Related Art

In recent years, accompanying the adoption of multimedia information incellular mobile communication systems, it has become common to transmitnot only speech data but also a large amount of data such as still imagedata and moving image data. Furthermore, studies have been activelyconducted in LTE-Advanced (Long Term Evolution Advanced) to realize hightransmission rates by utilizing broad radio bands, Multiple-InputMultiple-Output (MIMO) transmission technology, and interference controltechnology.

In addition, taking into consideration the introduction of variousdevices as radio communication terminals in M2M (machine to machine)communication and the like as well as an increase in the number ofmultiplexing target terminals due to MIMO transmission technology, thereis a concern regarding a shortage of resources in a mapping region forPDCCH (Physical Downlink Control Channel) that is used for a controlsignal (that is, a “PDCCH region”). If a control signal (PDCCH) cannotbe mapped due to such a resource shortage, downlink data cannot beassigned to the terminals. Therefore, even if a resource region in whichdownlink data is to be mapped (i.e., a “PDSCH (Physical Downlink SharedChannel) region”) is available, the resource region may not be used,which causes a decrease in the system throughput.

As a method for solving such a resource shortage, a study is being madeof assigning, in a data region, control signals for terminals served bya radio base station apparatus (hereunder, abbreviated as “basestation”). A resource region in which control signals for terminalsserved by the base station are mapped is referred to as an EnhancedPDCCH (ePDCCH) region, a New-PDCCH (N-PDCCH) region, an X-PDCCH regionor the like. Mapping the control signal (i.e., ePDCCH) in a data regionas described above enables transmission power control on control signalstransmitted to a terminal near a cell edge or interference control forinterference by a control signal to another cell or interference fromanother cell to the cell provided by the base station.

Further, according to the LTE-Advanced system, in order to expand thecoverage area of each base station, relay technology has been studied inwhich a radio communication relay station apparatus (hereunder,abbreviated as “relay station”) is installed between a base station andradio communication terminal apparatuses (hereunder, abbreviated as“terminals”; may also be referred to as UE (user equipment)), andcommunication between the base station and terminals is performed viathe relay station. The use of relay technology allows a terminal thatcannot communicate with the base station directly to communicate withthe base station via the relay station. According to the relaytechnology that has been introduced in the LTE-Advanced system, controlsignals for relay are assigned in a data region. Since it is expectedthat the control signals for relay may be extended for use as controlsignals for terminals, a resource region in which control signals forrelay are mapped is also referred to as an “R-PDCCH.”

In the LTE (Long Term Evolution) system, a DL grant (also referred to as“DL assignment”), which indicates a downlink (DL) data assignment, and aUL grant, which indicates an uplink (UL) data assignment are transmittedthrough a PDCCH. The DL grant indicates to the terminal that a resourcein the subframe in which the DL grant is transmitted has been allocatedto the terminal. On the other hand, the UL grant indicates to theterminal that a resource in a target subframe which is predetermined bythe UL grant has been allocated to the terminal.

In the LTE-Advanced system, a region (R-PDCCH for relay station (relayPDCCH) region) in which channel control signals for relay stations aremapped is provided in the data region. Similarly to the PDCCH, a DLgrant and UL grant are mapped to the R-PDCCH. In the R-PDCCH, the DLgrant is mapped in the first slot and the UL grant is mapped in thesecond slot (refer to Non-Patent Literature “hereunder abbreviated asNPL” 1). Mapping the DL grant only in the first slot reduces a delay indecoding the DL grant, and allows relay stations to prepare for ACK/NACKtransmission for DL data (transmitted in the fourth subframe followingreception of the DL grant in FDD). Thus, each relay station monitorschannel control signals transmitted using an R-PDCCH from a base stationwithin a resource region indicated by higher layer signaling from thebase station (i.e., a “search space”) and thereby finds the channelcontrol signal intended for the corresponding relay station.

In this case, the base station indicates the search space correspondingto the R-PDCCH to the relay station by higher layer signaling.

In the LTE and LTE-Advanced systems, one RB (resource block) has 12subcarriers in the frequency domain and has a width of 0.5 msec in thetime domain. A unit in which two RBs are combined in the time domain isreferred to as an RB pair (for example, see FIG. 1). That is, an RB pairhas 12 subcarriers in the frequency domain, and has a width of 1 msec inthe time domain. When an RB pair represents a group of 12 subcarriers onthe frequency axis, the RB pair may be referred to as simply “RB.” Inaddition, in a physical layer, an RB pair is also referred to as a PRBpair (physical RB pair). A resource element (RE) is a unit defined by asingle subcarrier and a single OFDM symbol (see FIG. 1).

Further, when the PDSCH is allocated to the RB, RBs may be allocated inunits of RBs or in units of RBGs (Resource Block Group). An RBG is aunit in which a plurality of adjacent RBs are arranged. Further, the RBGsize is defined by a bandwidth of a communication system, and LTE has 1,2, 3 and 4 as the defined RBG size.

A PDCCH and R-PDCCH have four aggregation levels, i.e., levels 1, 2, 4,and 8 (for example, see NPL 1). Levels 1, 2, 4, and 8 have six, six,two, and two “mapping candidates,” respectively. As used herein, theterm “mapping candidate” refers to a candidate region in which a controlsignal is to be mapped, and a search space is formed by a plurality ofmapping candidates. When a single aggregation level is configured for asingle terminal, a control signal is actually mapped in one of theplurality of mapping candidates of the aggregation level. FIG. 2illustrates an example of search spaces corresponding to an R-PDCCH. Theovals represent search spaces for the aggregation levels. The multiplemapping candidates in each search space for each aggregation level arelocated in a consecutive manner on VRBs (virtual resource blocks). Theresource region candidates in the VRBs are mapped to PRBs (physicalresource blocks) through higher layer signaling.

Studies are being conducted with respect to individually configuringsearch spaces corresponding to the ePDCCHs for terminals. Further, withrespect to the design of the ePDCCHs, part of the design of the R-PDCCHdescribed above can be used, and a design that is completely differentfrom the R-PDCCH design can also be adopted. In fact, studies are alsobeing conducted with regard to making the design of the ePDCCHs and thedesign of R-PDCCHs different from each other.

As described above, a DL grant is mapped to the first slot and a ULgrant is mapped to the second slot in an R-PDCCH region. That is, aresource to which the DL grant is mapped and a resource to which the ULgrant is mapped are divided on the time axis. In contrast, for theePDCCHs, studies are being conducted with regard to dividing resourcesto which DL grants are mapped and UL grants are mapped on the frequencyaxis (that is, subcarriers or PRB pairs), and with regard to dividingREs within an RB pair into a plurality of groups.

Further, the LTE-Advanced system supports carrier aggregation (CA). CAis a new function introduced in the LTE-Advanced system, which bundles aplurality of system bands termed component carriers (CCs) in LTE,thereby realizing an improvement in a maximum transmission rate (See NPL2). When a terminal uses a plurality of CCs, one CC is configured as aprimary cell (PCell) and a remaining CC is configured as a secondarycell (SCell). The configuration of the PCell and SCell may vary for eachterminal.

Further, a resource allocation method termed “cross-carrier scheduling”which performs an inter-cell interference control in units of CCs inPDCCH has been introduced in the LTE-Advanced system. In cross carrierscheduling, a base station can transmit DL grants and UL grants forother CCs in the PDCCH region of the CC having good channel quality (forexample, see FIG. 3B). If cross carrier scheduling is adopted, a PDCCHis transmitted from different a CC between adjacent cells, therebyallowing the inter-cell interference of PDCCH to be reduced.

In cross carrier scheduling, since resource allocation information istransmitted for each CC, the PDCCH increases in proportion to the numberof allocated CCs. Therefore, as the number of CCs increases, searchspaces are overlapped between different terminals, and thus theprobability of blocking (collision) increases. Furthermore, there is apossibility that blocking occurs not only between different terminalsbut also between PDCCHs of different CCs intended for a single terminal.The blocking between PDCCHs of the single terminal limits the number ofCCs that can be simultaneously allocated to the same terminal and limitsa maximum transmission rate for each terminal. Therefore, in PDCCHs ofthe LTE-Advanced system, a method is adopted in which at the time ofcalculating a search space, consecutive CCE regions different from eachother are configured as search spaces for CCs by using CIF (CarrierIndication Field) given to each of the CCs, in addition to UE IDs.

In addition, “localized allocation” which allocates ePDCCHs collectivelyat positions close to each other on the frequency band, and “distributedallocation” which allocates the ePDCCHs by distributing ePDCCHs on thefrequency band have been studied as allocation methods for ePDCCHs (forexample, see FIG. 4). The localized allocation is an allocation methodfor obtaining a frequency scheduling gain, and can be used to allocatean ePDCCH to a resource that has favorable channel quality based onchannel quality information. The distributed allocation distributesePDCCHs on the frequency axis, and can obtain a frequency diversitygain. In the LTE-Advanced system, both a search space for localizedallocation and a search space for distributed allocation may beconfigured (for example, see FIG. 4).

Furthermore, dividing each PRB pair into a plurality of resources in anePDCCH has been studied. Resources obtained by dividing the PRB pair maybe referred to as eCCEs (enhanced control channel elements) or eREGs(enhanced resource element groups). In addition, in the followingdescription, eCCEs may be simply referred to as “CCEs.” The number ofREs forming one CCE in a PDCCH is fixedly configured to 36 REs, but thenumber of REs forming one CCE in an ePDCCH varies depending on adivision method. As the division method, a division method in units ofsubcarriers or a division method by generating resource (RE) groups havebeen studied. FIG. 5 illustrates an example in which a plurality of PRBpairs are configured as search spaces for ePDCCHs and each PRB pair isdivided into four CCEs in units of subcarriers. In FIG. 5, CCEs obtainedby dividing each PRB pair are referred to as CCE#(4N), CCE#(4N+1),CCE#(4N+2), CCE#(4N+3), respectively (where, N=0, 1, 2, and 3).

CITATION LIST Non-Patent Literature

NPL 1

3GPP TS 36.216 V10.1.0 “Physical layer for relaying operation”

NPL 2

3GPP TS 36.213 V10.4.0 “Physical layer procedures”

BRIEF SUMMARY Technical Problem

The application of cross carrier scheduling even in the ePDCCHsdescribed above has been considered. However, the application of crosscarrier scheduling in the ePDCCHs has not been investigated so far.

An object of the present disclosure is to provide a transmissionapparatus, a reception apparatus, a transmission method, and a receptionmethod each of which makes it possible to properly perform cross carrierscheduling in ePDCCHs.

Solution to Problem

A transmission apparatus according to an aspect of the presentdisclosure includes: a configuration section that configures, whencommunication is performed using a plurality of component carriers(CCs), a first search space and a second search space within a samegroup of allocation units among a plurality of groups of allocationunits included in a data-assignable region within a first CC, the firstsearch space being a candidate to which control information for thefirst CC is assigned, the second search space being a candidate to whichcontrol information for a second CC other than the first CC among theplurality of CCs is assigned; and a transmission section that transmitscontrol information mapped to the first search space and controlinformation mapped to the second search space.

A reception apparatus according to an aspect of the present disclosureincludes: a configuration section that configures, when communication isperformed using a plurality of component carriers (CCs), a first searchspace and a second search space within a same group of allocation unitsamong a plurality of groups of allocation units included in adata-assignable region within a first CC, the first search space being acandidate to which control information for the first CC is assigned, thesecond search space being a candidate to which control information for asecond CC other than the first CC among the plurality of CCs isassigned; and a reception section that receives control informationmapped to the first search space and control information mapped to thesecond search space.

A transmission method according to an aspect of the present disclosureincludes: configuring, when communication is performed using a pluralityof component carriers (CCs), a first search space and a second searchspace within a same group of allocation units among a plurality ofgroups of allocation units included in a data-assignable region within afirst CC, the first search space being a candidate to which controlinformation for the first CC is assigned, the second search space beinga candidate to which control information for a second CC other than thefirst CC among the plurality of CCs is assigned; and transmittingcontrol information mapped to the first search space and controlinformation mapped to the second search space.

A reception method according to an aspect of the present disclosureincludes: configuring, when communication is performed using a pluralityof component carriers (CCs), a first search space and a second searchspace within a same group of allocation units among a plurality ofgroups of allocation units included in a data-assignable region within afirst CC, the first search space being a candidate to which controlinformation for the first CC is assigned, the second search space beinga candidate to which control information for a second CC other than thefirst CC among the plurality of CCs is assigned; and receiving controlinformation mapped to the first search space and control informationmapped to the second search space.

Advantageous Effects of Disclosure

According to the present disclosure, it is possible to properly performcross carrier scheduling in ePDCCHs.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram provided for describing a PRB pair;

FIG. 2 illustrates an example of search spaces corresponding toR-PDCCHs;

FIGS. 3A and 3B are diagrams illustrating non cross carrier schedulingand cross carrier scheduling, respectively;

FIG. 4 illustrates an example of localized allocation and distributedallocation of ePDCCHs;

FIG. 5 is a diagram provided for describing division of ePDCCHs.

FIG. 6 is a block diagram illustrating main components of a base stationaccording to Embodiment 1 of the present disclosure;

FIG. 7 is a block diagram illustrating main components of a terminalaccording to Embodiment 1 of the present disclosure;

FIG. 8 is a block diagram illustrating a configuration of the basestation according to Embodiment 1 of the present disclosure;

FIG. 9 is a block diagram illustrating a configuration of the terminalaccording to Embodiment 1 of the present disclosure;

FIG. 10 is a diagram illustrating a search space configuration accordingto Embodiment 1 of the present disclosure;

FIG. 11 is a diagram illustrating a search space configuration inconsideration of PRB bundling according to Embodiment 1 of the presentdisclosure;

FIGS. 12A and 12B are diagrams each illustrating a relationship betweenantenna ports and DMRS transmission power according to Embodiment 2 ofthe present disclosure;

FIG. 13 is a diagram illustrating a search space configuration accordingto Embodiment 2 of the present disclosure;

FIG. 14 is a diagram illustrating another search space configurationaccording to Embodiment 2 of the present disclosure;

FIG. 15 is a diagram illustrating a search space configuration accordingto Embodiment 3 of the present disclosure; and

FIG. 16 is a diagram illustrating a search space configuration accordingto a variation of the present disclosure.

DETAILED DESCRIPTION

Embodiments of the present disclosure will be described in detailhereunder with reference to the accompanying drawings. Throughout theembodiments, the same elements are assigned the same reference numerals,and any duplicate description of the elements is omitted.

Embodiment 1

[Communication System Overview]

A communication system according to the present embodiment includes atransmission apparatus and a reception apparatus. In particular, thepresent embodiment is described by taking base station 100 as thetransmission apparatus and taking terminal 200 as the receptionapparatus. The communication system is, for example, an LTE-Advancedsystem. Base station 100 is, for example, a base station that supportsthe LTE-Advanced system, and terminal 200 is, for example, a terminalthat supports the LTE-Advanced system.

FIG. 6 is a block diagram illustrating main components of base station100 according to the present embodiment.

In base station 100, when communication is performed using a pluralityof CCs, configuration section 102 configures a first search space thatis a candidate to which control information (a DL assignment, a ULgrant, and the like) for a first CC is assigned and a second searchspace that is a candidate to which control information for a second CCother than the first CC among the plurality of CCs is assigned, withinthe same allocation unit group among a plurality of allocation unitgroups (here, RBGs) included in a region to which data can be assigned(PDSCH region) (hereinafter, may be referred to as “data-assignableregion”) within the first CC

Transmission section 106 transmits control information mapped to thefirst search space and control information mapped to the second searchspace, the first and the second search spaces being configured byconfiguration section 102.

FIG. 7 is a block diagram illustrating main components of terminal 200according to the present embodiment.

In terminal 200, when communication is performed using a plurality ofCCs, configuration section 205 configures a first search space that is acandidate to which control information (a DL assignment, a UL grant, andthe like) for a first CC is assigned and a second search space that is acandidate to which control information for a second CC other than thefirst CC among the plurality of CCs is assigned, in the same allocationunit group among a plurality of allocation unit groups (here, RBGs)included in a data-assignable region (PDSCH region) within the first CC.

Control signal reception section 206 extracts control information mappedto each of the first search space and the second search space configuredby configuration section 205. Thus, control information transmitted frombase station 100 is received.

[Configuration of Base Station 100]

FIG. 8 is a block diagram illustrating a configuration of base station100 according to the present embodiment. As illustrated in FIG. 8, basestation 100 includes assignment information generation section 101,configuration section 102, error correction coding section 103,modulation section 104, signal assignment section 105, transmissionsection 106, reception section 107, demodulation section 108, and errorcorrection decoding section 109.

In a case where there is a downlink data signal (DL data signal) to betransmitted and an uplink data signal (UL data signal) to be assigned toan uplink (UL), assignment information generation section 101 determinesresources (RB) to which the data signals are assigned, and generatesassignment information (DL assignment and UL grant). The DL assignmentincludes information relating to assignment of the DL data signal. TheUL grant includes information relating to allocated resources for the ULdata signal to be transmitted from terminal 200. The DL assignment isoutputted to signal assignment section 105, and the UL grant isoutputted to reception section 107.

Configuration section 102 configures search spaces for a PCell and SCellwith respect to each terminal 200 using ePDCCHs, based on cross carrierscheduling information. The search spaces are formed by a plurality ofmapping candidates. Each of the “mapping candidates” is formed by CCEsof the same number as the value of the aggregation level. Further,“CCEs” are obtained by dividing each PRB pair into a predeterminednumber. For example, cross carrier scheduling information includesinformation relating to the PCell and SCell configured with respect toeach terminal 200.

For example, configuration section 102 determines search spaces (CCEsand RBs used for search spaces) of the PCell configured for terminal200. In addition, when cross carrier scheduling is configured withrespect to terminal 200, configuration section 102 determines searchspaces for the SCell based on the search spaces for the PCell,calculation equations that are held in advance, and values (for example,CIF) by which the SCell can be identified. In the above calculationequations, PRB pairs within the same RBG are preferentially configuredas search spaces such that the ePDCCHs intended for the same terminalare to be transmitted in the same RBG. In addition, in the abovecalculation equations, the search spaces for the SCell are configured inthe PRB pair obtained by shifting the PRB pair in which the searchspaces for the PCell are configured using CIF so that the search spacesfor CCs, to which control information transmitted from the same CC aremapped, do not collide. Note that process of configuring a search spaceperformed by configuration section 102 is described in detailhereinafter.

Configuration section 102 outputs information relating to a search spacewhich has been configured (hereinafter, may also be referred to as“search space information”) to signal assignment section 105.Configuration section 102 also outputs information relating to PRB pairsthat have been configured as a search space for the PCell to errorcorrection coding section 103 as control information.

Error correction coding section 103 receives a transmission data signal(DL data signal) and control information received from configurationsection 102 as input signals, performs error correction coding on theinput signals, and outputs the processed signals to modulation section104.

Modulation section 104 modulates the signals received from errorcorrection coding section 103, and outputs the modulated data signal tosignal assignment section 105.

Signal assignment section 105 assigns the assignment information (DLassignment and UL grant) received from assignment information generationsection 101 to any CCE among CCEs (CCEs in mapping candidate units)indicated by search space information received from configurationsection 102. Signal assignment section 105 also assigns the data signalreceived from modulation section 104 to a downlink resourcecorresponding to the assignment information (DL assignment) receivedfrom assignment information generation section 101.

A transmission signal is formed by assignment information and a datasignal being assigned to predetermined resources in this manner. Thethus-formed transmission signal is outputted to transmission section106.

Transmission section 106 executes radio transmission processing such asup-conversion on the input signal, and transmits the obtained signal toterminal 200 via an antenna.

Reception section 107 receives a signal transmitted from terminal 200via an antenna, and outputs the received signal to demodulation section108. More specifically, reception section 107 separates a signal thatcorresponds to a resource indicated by a UL grant received fromassignment information generation section 101 from the received signal,and executes reception processing such as down-conversion on theseparated signal and thereafter outputs the obtained signal todemodulation section 108.

Demodulation section 108 executes demodulation processing on the inputsignal, and outputs the obtained signal to error correction decodingsection 109.

Error correction decoding section 109 decodes the input signal to obtainthe received data signal from terminal 200.

[Configuration of Terminal 200]

FIG. 9 is a block diagram illustrating the configuration of terminal 200according to the present embodiment. As illustrated in FIG. 9, terminal200 includes reception section 201, signal separating section 202,demodulation section 203, error correction decoding section 204,configuration section 205, control signal reception section 206, errorcorrection coding section 207, modulation section 208, signal assignmentsection 209, and transmission section 210.

Reception section 201 receives a signal transmitted from base station100 via an antenna, and after executing reception processing such asdown-conversion on the received signal, outputs the processed signal tosignal separating section 202.

Signal separating section 202 extracts a control signal relating toresource allocation from the reception signal received from receptionsection 201, and outputs the extracted signal to control signalreception section 206. Signal separating section 202 also extracts fromthe reception signal a signal corresponding to a data resource (that is,a DL data signal) indicated by the DL assignment output from controlsignal reception section 206, and outputs the extracted signal todemodulation section 203.

Demodulation section 203 demodulates the signal outputted from signalseparating section 202, and outputs the demodulated signal to errorcorrection decoding section 204.

Error correction decoding section 204 decodes the demodulated signaloutputted from demodulation section 203, and outputs the obtainedreceived data signal. In particular, error correction decoding section204 outputs “information relating to PRB pairs configured as searchspaces for the PCell” transmitted as a control signal from base station100, to configuration section 205.

Configuration section 205 specifies search spaces configured forterminal 200 of configuration section 205 that uses the ePDCCHs, basedon cross-carrier scheduling information. For example, first,configuration section 205 specifies PRB pairs configured as the searchspaces for the PCell based on information received from error correctiondecoding section 204. Next, configuration section 205 specifies searchspaces for the SCell, based on the search spaces for the PCell, acalculation equation held in advance, and a value (for example, a CIF)by which the SCell can be identified. The above calculation equation isshared between base station 100 and terminal 200. In other words, in asimilar manner to configuration section 102, configuration section 205configures the search spaces for terminal 200 of configuration section205. Configuration section 205 outputs information relating to PRB pairsand CCEs configured as the search space to control signal receptionsection 206. In addition, search space configuration processingperformed by configuration section 205 is described in detail later.

In a signal component received from signal separating section 202,control signal reception section 206 detects a control signal (DLassignment or UL grant) intended for terminal 200 of signal separatingsection 202 by performing blind decoding with respect to CCEs indicatedby information received from configuration section 205. That is, controlsignal reception section 206 receives a control signal mapped to onemapping candidate among a plurality of mapping candidates forming asearch space configured by configuration section 205. Control signalreception section 206 outputs a detected DL assignment intended forterminal 200 of control signal reception section 206 to signalseparating section 202, and outputs a detected UL grant intended forterminal 200 of control signal reception section 206 to signalassignment section 209.

When a transmission data signal (UL data signal) is inputted to errorcorrection coding section 207, error correction coding section 207performs error correction coding on the transmission data signal andoutputs the obtained signal to modulation section 208.

Modulation section 208 modulates the signal outputted from errorcorrection coding section 207, and outputs the modulated signal tosignal assignment section 209.

Signal assignment section 209 assigns the signal outputted frommodulation section 208 according to the UL grant received from controlsignal reception section 206, and outputs the obtained signal totransmission section 210.

Transmission section 210 executes transmission processing such asup-conversion on the input signal, and transmits the obtained signal.

[Operations of Base Station 100 and Terminal 200]

The operations of base station 100 and terminal 200 each configured inthe manner described above will be described.

In the following description, it is assumed that a plurality of CCs areconfigured for terminal 200. Further, it is assumed that an ePDCCH isused as an allocated resource of control information intended forterminal 200 (DL assignment or UL grant), and cross carrier schedulingis configured for the ePDCCH. Furthermore, in cross carrier scheduling,it is assumed that a CC to which control information for each CCconfigured for terminal 200 is assigned is the PCell. In other words,search spaces to which control information for the PCell intended forterminal 200 are assigned and search spaces to which control informationfor the SCell are assigned are configured in the PCell.

Here, in the ePDCCH, similar to the case of a PDCCH, blocking betweenthe ePDCCHs of CCs needs to be reduced. Since the ePDCCHs are mapped ina PDSCH region (data-assignable region), blocking with a PDSCH needs tobe reduced in addition to the blocking between the ePDCCHs.

As described above, the PDSCH is assigned in RBG units. Accordingly,base station 100 cannot assign data as a PDSCH to a terminal whichcannot recognize the presence of the ePDCCH, for example, terminals ofrel. 8, 9, and 10 in an RBG including a PRB pair used as the ePDCCH.Therefore, it is preferable to ensure a larger number of RBGs that canbe used as a PDSCH by further reducing RBGs including PRB pairs used forePDCCHs.

Therefore, in the present embodiment, when cross carrier scheduling isapplied to ePDCCHs, configuration section 102 of base station 100preferentially configures search spaces for ePDCCHs of a plurality ofCCs configured for terminal 200 within the same RBG. Specifically,configuration section 102 configures search spaces for the ePDCCH forthe PCell and search spaces for the ePDCCH for the SCell, within thesame RBG, among a plurality of RBGs included in a PDSCH region withinthe PCell configured for terminal 200. At this time, configurationsection 102 configures different PRB pairs within the same RBG to searchspaces for the ePDCCH for the PCell and search spaces for the ePDCCH forthe SCell.

As a search space configuration example at the time of cross carrierscheduling in the present embodiment, a description will be given of acase where a CIF value (CIF number) configured in each CC is used.

Specifically, within the same RBG, the configuration section 102configures PRB pairs (PRB pairs different from the PRB pairs configuredas the search spaces for the PCell) obtained by cyclically shifting thePRB pairs configured as the search spaces for the PCell, as the searchspaces for the SCell. In this case, configuration section 102 uses theCIF number configured in each SCell as the amount of the cyclic shift.In other words, configuration section 102 configures PRB pairs obtainedby cyclically sifting the PRB pairs of the PCell by the value of the CIFnumber configured for each SCell, within the same RBG as the RBG towhich PRB pairs configured as the search space for a reference CC (here,the PCell) belong, as the search spaces for the SCell having the CIFnumber.

Further, in a case where the CIF number (it is assumed that CIF=0, 1, 2,. . . ) corresponding to the cyclic shift value is equal to or greaterthan the RBG size (the number of PRB pairs forming one RBG),configuration section 102 configures a PRB pair within another RBGadjacent to the RBG to which the PRB pairs configured as the searchspace for the PCell belongs, as the search space for the SCell havingthe CIF number. In other words, configuration section 102 shifts thesearch space for the SCell corresponding to the CIF number equal to orgreater than the RBG size, an RB within an RBG adjacent to the RBG inwhich the search space for the PCell is configured.

For example, configuration section 102 configures the search spaces forthe SCell according to Equation 1 below.[1]N _(RB,n) _(CL) =floor(n _(CL)/RBGsize)·RBGsize+N _(RBG,0)·RBGsize+(N_(RB,0) +n _(CL))mod(RBGsize)  (Equation 1)

In Equation 1, n_(CL) indicates the CIF number (n_(CL)=0, 1, 2, . . . ),N_(RB,nCL) indicates an RB number of the search space for CC of whichthe CIF number is n_(CL), N_(RB,0) indicates the RB number (PRB pairnumber) of the search spaces for the PCell (n_(CL)=0) that is areference CC, and N_(RBG,0) indicates the RBG number with which thesearch spaces for the PCell (n_(CL)=0) are configured. In addition, afunction floor (x) indicates a function that returns a value obtained byrounding off to the nearest whole number x, and an operator modindicates a modulo operation.

The first term of Equation 1 [floor(n_(CL)/RBGsize)·RBGsize] indicates ashift value in RBG units from the PCell with respect to the search spacefor the SCell of which the CIF number is n_(CL). For example, if thevalue of the first term is 0, the search space is configured within thesame RBG as the PCell.

The second term [N_(RBG,0)·RBGsize] of Equation 1 indicates the smallestRB number among RB numbers of PRB pairs forming the RBG (RBG number isN_(RBG,0)) in which the search space for the PCell is configured, andbecomes a reference value of a shift value of RB number.

The third term of Equation 1 [(N_(RB,0)+n_(CL)) mod (RBGsize)] indicatesa shift value within the RBG from the RB number corresponding to PRBpairs configured as the search space (N_(RB,0)) of the PCell, withrespect to the search space for the SCell of which the CIF number isn_(CL).

That is, the second and third terms of Equation 1 indicate a cyclicshift.

Thus, the search space for each CC at the time of cross carrierscheduling is configured to different PRB pairs obtained by cyclicallyshifting the PRB pair within the same RBG as PRB pairs configured as thesearch spaces for the PCell, by the value of the CIF number. Inaddition, when the CIF number is equal to or greater than the RBG size,the search space for the SCell having the CIF number is configured in aPRB pair within the RBG adjacent to the RBG in which the search spacesfor the PCell are configured.

FIG. 10 is a diagram illustrating a search space configuration exampleat the time of cross carrier scheduling in a case where a PCell and twothe SCells are configured for terminal 200.

In FIG. 10, it is assumed that the RBG size is 3 (RBG size=3), the CIFnumber of one SCell is 1 (CIF=1), and the CIF number of the other SCellis 3 (CIF=3). Further, in FIG. 10, it is assumed that the aggregationlevel is 4. Furthermore, as illustrated in FIG. 10, the search spacesfor the PCell (CIF=0) are configured in RB#1 (CCE0 to CCE3) belonging toRBG#0 and RB#7 (CCE4 to CCE7) belonging to RBG#2.

First, the SCell of CIF=1 (less than RBG size (=3)) is described. Asillustrated in FIG. 10, configuration section 102 configures RB#2 andRB#8 obtained by cyclically shifting RB#1 and RB#7 configured as thesearch spaces for the PCell by the value of the CIF number (that is, oneRB), as the search spaces for the SCell of CIF=1. As illustrated in FIG.10, the PRB pairs (RB#1, RB#7) configured as the search spaces for thePCell and the PRB pairs (RB#2, RB#8) configured as the search spaces forthe SCell of CIF=1 are to be respectively configured within the sameRBGs (RBG#0 and RBG#2) and are different from each other.

Subsequently, the SCell of CIF=3 (equal to or greater than RBG size(=3)) is described. As illustrated in FIG. 10, configuration section 102cyclically shifts RB#1 and RB#7 in which the search spaces for the PCellare configured, by the value of the CIF number (that is, three RBs), atthe time of configuring the search spaces for the SCell of CIF=3.However, since the CIF number (=3) is equal to or greater than the RBGsize (RBG size=3), configuration section 102 configures the searchspaces for the SCell of CIF=3 within RBG#1 and RBG#3 respectivelyadjacent to RBG#0 and RBG#2 in which the search spaces for the PCell areconfigured. In other words, configuration section 102 configures thesearch spaces for the SCell of CIF=3, in RB#4 belonging to RBG#1 andRB#10 belonging to RBG#3.

In other words, as illustrated in FIG. 10, the search spaces for theSCell having the CIF numbers (CIF=1, 2) less than the RBG size arerespectively configured in cyclically shifted different PRB pairs withinthe RBGs to which the PRB pairs configured as the search spaces for thePCell (CIF=0) belong. On the other hand, the search spaces for the SCellhaving the CIF numbers (CIF=3, 4) equal to or greater than the RBG sizeare respectively configured within the RBGs adjacent to the RBGs towhich the PRB pairs configured as the search spaces for the PCell(CIF=0) belong. At this time, as illustrated in FIG. 10, the searchspaces for the SCell are respectively configured in PRB pairs cyclicallyshifted from, as the starting point, the PRB pairs (RB#4 of RBG#1 andRB#10 of RBG#3) corresponding to the position (that is, the second RBfrom the minimum RB number within the RBG) of RB#1 (and RB7 of RBG#2) inRBG#0 in which the search spaces for the PCell are configured, in theadjacent RBG.

Circled numbers ‘0’ to ‘4’ illustrated in FIG. 10 represent a cyclicshift pattern (shift order) relative to the PRB pairs configured as thesearch space for the PCell (corresponding to circled number ‘0’, RB#1 inFIG. 10).

On the other hand, similar to configuration section 102, configurationsection 205 of terminal 200 specifies search spaces for each CCconfigured for terminal 200. Specifically, first, configuration section205 acquires information (for example, RBG number and RB number)relating to PRB pairs configured as the search spaces for the PCell,from base station 100. Subsequently, configuration section 205configures the PRB pairs obtained by cyclically shifting PRB pairsconfigured as the search spaces for the PCell, by the value of the CIFnumber configured in each SCell, as the search spaces for the SCell.Further, when the CIF number is equal to or greater than the RBG size,configuration section 205 configures the search spaces for the SCellwithin the RBGs respectively adjacent to RBGs to which the PRB pairsconfigured as the search spaces for the PCell belong. For example,configuration section 205 configures the search spaces for the SCellbased on RBs configured as the search spaces for the PCell and acalculation Equation (Equation 1) which is held in advance.

As described above, in the present embodiment, when communication withterminal 200 is performed using a plurality of CCs, base station 100 andterminal 200 configure search spaces as candidates to which controlinformation for the PCell is assigned and search spaces as candidates towhich control information for SCells (CCs other than PCell) is assignedin the same RBG among a plurality of RBGs, each of which is formed by aplurality of PRB pairs included in the PDSCH region within the PCell.

Thus, since the search spaces for ePDCCHs at the time of cross carrierscheduling tends to be configured in RBG units, it is possible to securemore RBGs to which data can be assigned in the PDSCH region. In otherwords, according to the present embodiment, it is possible to reduce ablocking occurrence rate of PDSCH to be allocated in RBG units and thesearch spaces for ePDCCHs.

Further, in the present embodiment, base station 100 and terminal 200configure different PRB pairs within the same RBG as search spaces forthe ePDCCH of each CC. This enables the reduction of a blockingoccurrence rate between the ePDCCHs of the same aggregation level ofeach CC.

Furthermore, according to the present embodiment, since the searchspaces for other CCs (SCells) are configured based on the search spacesfor the PCell, compared to a case where the search spaces areindividually configured for each CC, it is possible to reduce the numberof bits of a higher layer necessary for configuring the search spaces.Further, in the present embodiment, at the time of search spaceconfiguration, the CIF number of each CC that is an existing parameteris used as a parameter for determining a cyclic shift value from thesearch spaces for the PCell. Thus, since there is no need to newly use aparameter for the search space configuration, it is possible to avoidincreases in the number of bits necessary for configuring the searchspaces.

Furthermore, according to the present embodiment, in a case where theCIF number is equal to or greater than the RBG size, the search spacesfor the SCell having the CIF number is shifted to the RB within the RBGadjacent to the RBG in which the search spaces for the PCell areconfigured. Thus, even in a case where the CIF number is equal to orgreater than the RBG size, the search spaces for the SCell cannot beconfigured within the same RBG as the search spaces for the PCell, andthe search spaces for the SCell can be configured in resources expectedto have relatively the same channel quality as the search spaces for thePCell. Since search spaces corresponding to a plurality of CCsconfigured for terminal 200 are configured in resources having the samedegree of channel quality, an aggregation level, a transmission method(for example, presence or absence of transmission diversity), and thelike which are selected in each CC can be matched between CCs, therebyfacilitating the scheduling processes of base station 100.

In the manner described above, according to the present embodiment, thecross carrier scheduling can be properly performed even with ePDCCHs.

In addition, the present embodiment has been described with a case wherethe RBG size is three, but the RBG size is not limited to three.

For example, RBG size may be four. In addition, when the RBG size isfour, a shift pattern may be determined with respect to the searchspaces for the PCell in consideration of units of PRB bundling. The term“PRB bundling” is a technique that uses the same pre-coding in aplurality of adjacent PRB pairs for improving the channel estimationaccuracy, in a case where a DMRS (DeModulation Reference Signal) servingas a reference signal and allowing a different beam to be directed toeach terminal is used. The unit (PRB bundling unit) using the samepre-coding is called a PRG (Pre-coding Resource block Group). The sizeof PRG (PRG size) is the same as the RBG size and different values areset depending on the number of PRB pairs included in a system bandwidth. For example, when the RBG size is four or two, the PRG size istwo, and when the RBG size is three, PRG size is three. Accordingly,when the RBG size is four, four PRB pairs included in the same RBG formone PRG for each two PRB pairs (see FIG. 11). Therefore, only two PRBpairs within the same RBG are used for ePDCCHs, and when two remainingPRB pairs are allocated to PDSCH, two PRB pairs belonging to PRGsupposedly using the same pre-coding are preferably allocated to thePDSCH.

In this respect, when the RBG size is four, for example, base station100 and terminal 200 may preferentially configure the search spaces forthe SCell in PRB pairs within the PRG to which PRB pairs configured asthe search spaces for the PCell belong. In other words, among two PRBpairs forming the same PRG, base station 100 and terminal 200 configureone PRB pair as a search space for the PCell and configure the other PRBpair as a search space for the SCell.

For example, base station 100 and terminal 200 may configure a shiftorder of RBs (shift pattern) in such a way as to preferentially shift aPRB pair configured as the search space for the PCell within a PRG towhich the PRB pair belongs, and then a shift is made within the RBG towhich the PRB pair belong. In FIG. 11, the PRB pair within the PRG towhich the PRB pair configured as the search space for the PCell (CIF=0)belongs, is configured as the search space for the SCell of CIF=1.Subsequently, PRB pairs within the RBG to which the PRB pair configuredas the search space for the PCell (CIF=0) belongs and PRG pairs otherthan the PRG to which PRB pair configured as the search space for thePCell (CIF=0) belongs are configured as the search spaces for the SCellsof CIF=2, 3. The two drawings in FIG. 11 illustrate resources (that is,the same resources) to which signals to be transmitted in downlink ofthe PCell are mapped. For convenience of description, FIG. 11illustrates search spaces for the CCs configured within one CC (PCell)while the search spaces are classified for the CCs. Circled numbers ‘0’to ‘3’ illustrated in FIG. 11 represent a cyclic shift pattern based onthe PRB pair configured as the search space for the PCell (circlednumber ‘0’).

Further, in the present embodiment, a description has been given of acase where search spaces are configured in consideration of RBGs, thepresent disclosure is not limited to this case. For example, searchspaces may be configured in consideration of units of sub-bands used atthe time of reporting a sub-band CQI. Here, the units of sub-bands areunits of PRB pairs used for averaging the channel quality when theterminal reports the channel quality to the base station. For example, asub-band is formed of six PRB pairs. For example, when localizedallocation is used as the resource allocation method, the base stationcan determine a PRB pair used for transmitting an ePDCCH based on thechannel quality report. In addition, when the feedback of channelquality is provided in units of sub-bands, the PRB pairs belonging tothe same sub-band are regarded to have the same channel quality by thebase station. Therefore, base station 100 and terminal 200 may configuresearch spaces for a plurality of CCs within the same sub-band (that is,different PRB pairs within the same sub-band). In other words, basestation 100 and terminal 200 may configure the search spaces for anSCell by cyclically shifting PRB pairs configured as the search spacefor the PCell within the PRB pairs of the same sub-band, in preferenceto the PRB pairs of the same RBG. In this manner, the ePDCCHs of aplurality of CCs can be mapped to RBs that are expected to have the samechannel quality, so that the reception quality between the ePDCCHs ofCCs does not change, and it is not necessary to change the selection ofthe aggregation levels of the ePDCCHs for each CC.

Although the present embodiment describes a case where the search spacesfor the SCell are configured by cyclically shifting PRB pairs configuredas the search spaces for the PCell, the configuration of the searchspaces for the SCell is not limited to the case using the cyclic shift.In other words, a method may be applied in which with respect to PRBpairs configured as the search spaces for the PCell, different PRB pairsbelonging to the same RBG are preferentially configured as the searchspaces for the SCell.

Embodiment 2

The present embodiment relates to a search space configuration methodfocused on power of reference signals. Since a base station and aterminal according to the present embodiment have the same basicconfiguration as base station 100 and terminal 200 according toEmbodiment 1, a description will be given with references made to FIGS.8 and 9.

In the LTE-Advanced system, demodulating ePDCCH using DMRS (DeModulationReference Signal) with which pre-coding can be changed for each terminalas reference signals has been studied. Since configuring a plurality ofantenna ports to which DMRSs are assigned in the same PRB pair (forexample, see FIG. 1) makes possible application of MIMO (Multiple InputMultiple Output) transmission.

Further, transmitting the ePDCCHs by multiplexing the ePDCCHs intendedfor a plurality of terminals in the same PRB pair has been studied inLTE-Advanced. At this time, if different pre-coding is applied for eachterminal, it is necessary to respectively transmit DMRSs assigned to thedifferent antenna ports.

However, when DMRSs are transmitted from a plurality of antenna ports inthe same PRB pair, there is a problem in that the transmission power ofeach antenna port needs to be reduced. FIGS. 12A and 12B each illustratea relationship between antenna ports and transmission power of DMRSs.FIG. 12A illustrates a case where all CCEs (CCE0 to CCE3) in the PRBpair are allocated to the same terminal (UE#0) and only an antenna port7 (port7) is used. FIG. 12B illustrates a case where all CCEs (CCE0 toCCE3) in the PRB pair are respectively allocated to different terminals(UE#0 to UE#3) and antenna ports 7, 8, 9, and 10 are used. In FIGS. 12Aand 12B, it is assumed that the total transmission power of all antennaports is constant.

As illustrated in FIG. 12A, when only the antenna port 7 is used,compared to the case where the antenna ports 7, 8, 9, and 10 are used asillustrated in FIG. 12B, the transmission power of DMRSs per antennaport (port7) can be quadrupled and used. In other words, in the same PRBpair, as the number of terminals decreases, the number of antenna portsto be used decreases, and an increase in transmission power by powerboosting becomes possible.

The reception quality of DMRS is very important for improving thechannel estimation accuracy, and increasing the transmission power ofDMRS is very effective for improving the reception quality of theePDCCH.

Therefore, in the present embodiment, when cross carrier scheduling isapplied to the ePDCCH, configuration section 102 of base station 100preferentially configures the search spaces (CCEs) of the ePDCCHs of aplurality of CCs configured for terminal 200 in the same PRB pair.Specifically, configuration section 102 configures the search spaces forthe ePDCCH for the PCell and the search spaces for the ePDCCH for theSCell in the same PRB pair among a plurality of PRB pairs included inthe PDSCH region within the PCell configured for terminal 200. At thistime, configuration section 102 configures different CCEs (eREGs) in thesame PRB pair as the search spaces for the ePDCCH for the PCell and thesearch spaces for the ePDCCH for the SCell.

Further, when the search spaces for the ePDCCH of a plurality of CCs areconfigured within the same PRB pair, configuration section 102configures DMRS allocated to the same antenna port as a reference signalof an ePDCCH of each CC.

Similar to Embodiment 1, when a CIF number configured in each CC is usedwill be described as an example of search space configuration at thetime of cross carrier scheduling in the present embodiment.

Specifically, configuration section 102 configures CCEs (CCEs differentfrom the CCEs which are configured in the search spaces for the PCell)obtained by cyclically shifting the CCEs which are configured as thesearch spaces for the PCell in the same PRB pair, as the search spacesfor the SCell. At this time, configuration section 102 uses the CIFnumber configured in each SCell as a cyclic shift amount. In otherwords, configuration section 102 configures CCEs obtained by cyclicallysifting the CCEs of the PCell by the CIF number configured in eachSCell, as the search space for the SCell having the CIF number, in thesame PRB pair as the CCEs configured as the search space for a basic CC(here, the PCell).

In addition, when the CIF number (it is assumed that CIF=0, 1, 2, . . .) corresponding to the cyclic shift value is equal to or greater thanthe number of CCEs forming the PRB pair, configuration section 102configures CCEs within another PRB pair adjacent to the PRB pair towhich the CCEs configured as the search space for the PCell belongs, asthe search space for the SCell having the CIF number. In other words,configuration section 102 shifts the search space for the SCellcorresponding to the CIF number equal to or greater than the number ofCCEs forming the PRB pair, to the CCEs within an PRB pair adjacent tothe PRB pair configured as the search space for the PCell.

For example, configuration section 102 configures the search spaces forthe SCell, according to Equations 2 and 3. Further, Equation 2 indicatesthe eREG numbers in which CCEs configured as the search spaces aremapped, and Equation 3 indicates PRB pair numbers (RB numbers)configured as the search spaces. Furthermore, in the present embodiment,the eREG numbers are defined as the numbers given within one PRB pair,and the eREG size is assumed to eREG division number per one PRB pair.Accordingly, in a case where the eREG division number is K, the eREGnumbers are #0 to # (K−1).[2]N _(eREG,n) _(CL) =(N _(eREG,0) +n _(CL))mod(eREGsize)  (Equation 2)[3]N _(RB,n) _(CL) =floor(n _(CL) /eREGsize)+N _(RB,0)  (Equation 3)

In Equation 2 and Equation 3, n_(CL) indicates CIF number (n_(CL)=0, 1,2, . . . ), N_(RB,nCL) indicates RB numbers of the search spaces for CCof which CIF number is n_(CL), N_(RB,0) indicates RB numbers of thesearch spaces for the PCell (n_(CL)=0) that is a reference CC, N_(RBG,0)indicates the RBG number in which the search spaces for the PCell(n_(CL)=0) are configured, N_(eREG,0) indicates an eREG number in whichthe search spaces for the PCell (n_(CL)=0) is configured, andN_(eREG,nCL) indicates eREG numbers in which the search spaces for CC,of which CIF number is n_(CL), are configured. In addition, eREG size isa division number of eREG per one PRB pair and has the same number asthe number of CCEs (CCE division number) per PRB pair. In addition, afunction floor (x) indicates a function that returns a value obtained byrounding off to the nearest whole number x, and operator mod indicates amodulo operation.

Thus, the search spaces for each CC at the time of cross carrierscheduling is configured in the different eREGs obtained by cyclicallyshifting eREGs corresponding to the CCEs by the CIF number in the PRBpair to which the CCEs configured as the search spaces for the PCellbelongs. In addition, in a case where the CIF number is equal to orgreater than the number of CCEs (eREG division number) forming one PRBpair, the search spaces for the SCell having the CIF number areconfigured in CCEs (eREGs) within the PRB pair adjacent to the PRB pairconfigured as the search spaces for the PCell.

FIG. 13 illustrates an example of search space configuration at crosscarrier scheduling when one PCell and two SCells are configured forterminal 200. Three drawings illustrated in FIG. 13 show resources (thatis, the same resources) in which signals transmitted in downlink of thePCell are mapped. In other words, for the convenience of explanation,FIG. 13 separately shows for each CC, the search spaces for three CCsconfigured within one CC (PCell).

In FIG. 13, it is assumed that the CIF number of one SCell is 1 (CIF=1),and the CIF number of the other SCell is 4 (CIF=4). Further, in FIG. 13,it is assumed that the aggregation level is 1. Furthermore, in FIG. 13,it is assumed that the number of eREGs (eREG division number) per PRBpair is four (eREG size=4). Furthermore, as illustrated in FIG. 13, thesearch spaces for the PCell (CIF=0) are configured in eREG#0 (CCE0)belonging to RB#1, eREG#1 (CCE5) belonging to RB#4, eREG#2 (CCE10)belonging to RB#7, and eREG#3 (CCE15) belonging to RB#10.

First, the SCell of CIF=1 (less than eREG division number 4) will bedescribed. As illustrated in FIG. 13, configuration section 102configures eREG#1 (CCE0) in RB#1 obtained by cyclically shifting theeREG#0 in RB#1 configured as the search space for the PCell by a CIFnumber amount (that is, one eREG), as the search space for the SCell ofCIF=1. In a similar manner, as illustrated in FIG. 13, configurationsection 102 configures eREG#2 (CCE5) in RB#4 obtained by cyclicallyshifting the eREG#1 in RB#4 configured as the search space for the PCellby one eREG, as the search space for the SCell of CIF=1. The searchspace for the SCell with respect to other PRB pairs (RB#7 and RB#10)configured as the search space for the PCell as illustrated in FIG. 13is obtained in a similar manner.

As illustrated in FIG. 13, CCEs (eREGs) in which the search spaces forthe PCell are configured and CCEs (eREG) in which the search spaces forthe SCell of CIF=1 are configured are to be configured in the same PRBpairs (RB#1, RB#4, RB#7 and RB#10). Therefore, configuration section 102configures DMRSs assigned to the same antenna port with respect to theePDCCHs for the PCell and the SCell of CIF=1. In other words, theantenna port allocated to DMRSs for the ePDCCHs to be transmitted in thesearch spaces for the PCell and the antenna port allocated to DMRSs forthe ePDCCHs to be transmitted in the search spaces for the SCell are thesame.

Further, as illustrated in FIG. 13, the search spaces CCEs of the PCelland the search spaces for the SCell of CIF=1 are configured in differentCCEs (eREGs) within the same PRB pair (RB#1, RB#4, RB#7 and RB#10).

Next, the SCell of CIF=4 (equal to or greater than eREG division number4) will be described. As illustrated in FIG. 13, at the time ofconfiguring the search spaces for the SCell of CIF=4, configurationsection 102 cyclically shifts eREG#0 in RB#1 configured as the searchspace for the PCell by the value of the CIF number (that is, 4 eREGs).However, since the CIF number (=4) is eREG size (eREG size=4) orgreater, configuration section 102 configures the search space for theSCell of CIF=4 within RBG#2 adjacent to RB#1 in which the search spacefor the PCell is configured. In other words, configuration section 102configures eREG#0 (CCE0) in RB#2 as the search space for the SCell ofCIF=4. In the same manner, as illustrated in FIG. 13, configurationsection 102 configures eREG#1 (CCE5) of RB#5 obtained by shifting eREG#1in RB#4 configured as the search space for the PCell by 4 eREGs, as thesearch space for the SCell of CIF=4. The search spaces for the SCellwith respect to other PRB pairs (RB#7 and RB#10) in which the searchspaces for the PCell are configured as illustrated in FIG. 13 areobtained in a similar manner.

On the other hand, in the same manner as configuration section 102,configuration section 205 of terminal 200 specifies the search spacesfor each CC configured for terminal 200. Specifically, first,configuration section 205 acquires information relating to PRB pairs andeREGs configured as the search spaces for the PCell from base station100. Subsequently, configuration section 205 configures eREGs obtainedby cyclically shifting the eREGs configured as the search spaces for thePCell within PRB pairs configured as the search spaces for the PCell, bythe value of the CIF number configured in each SCell, as the searchspaces for the SCell having the CIF number. In addition, when the CIFnumber is equal to or greater than the eREG size, configuration section205 configures the search spaces for the SCell having the CIF number ineREGs within the PRB pairs adjacent to the PRB pairs configured as thesearch spaces for the PCell. For example, configuration section 205configures the search spaces for the SCell, based on RBs and eREGsconfigured as the search spaces for the PCell and calculation equations(Equations 2 and 3) held in advance.

As described above, in the present embodiment, when communication isperformed with terminal 200 using a plurality of CCs, base station 100and terminal 200 configure the search spaces as candidates in whichcontrol information for the PCell is assigned and the search spaces ascandidates in which control information for the SCell (CC other than thePCell) is assigned, in the same PRB pairs among a plurality of PRB pairseach of which is formed of a plurality of CCEs included in the PDSCHregion in the PCell.

Thus, preferentially configuring the search spaces for the ePDCCHs of aplurality of CCs configured for terminal 200 in the same PRB pairs makesit possible to transmit DMRS using a less number of antenna ports (forexample, see FIG. 12A). This enables an increase in transmission powerof DMRS by power boosting for one terminal 200 and leads to animprovement in the channel estimation accuracy of the ePDCCHs.

Further, similar to Embodiment 1, since base station 100 and terminal200 each configure the different eREGs in the same PRB pairs as thesearch spaces for the ePDCCHs of each CC, it is possible to reduce theblocking occurrence rate between the ePDCCHs of each CC.

According to the present embodiment, similar to Embodiment 1, at thetime of configuring search spaces, the CIF number of each CC that is anexisting parameter is used as a parameter for determining a cyclic shiftvalue from the search spaces for the PCell. Thus, since there is no needto newly use a parameter for the search space configuration, it ispossible to avoid increases in the number of bits necessary forconfiguring the search spaces.

Further, according to the present embodiment, in a case where the CIFnumber is the eREG division number (CCE division number) or greater, thesearch spaces for the SCell having the CIF number are shifted to eREGswithin the PRB pairs adjacent to the PRB pairs in which the searchspaces for the PCell are configured. Thus, similar to Embodiment 1, thesearch spaces for the SCell can be configured in resources which areexpected to have relatively the same channel quality as the resources ofthe search spaces for the PCell. In this manner, the search spacescorresponding to a plurality of CCs configured for terminal 200 areconfigured in resources having the same degree of channel quality, sothat an aggregation level, a transmission method (for example, presenceor absence of transmission diversity), and the like to be selected foreach CC can be matched between CCs, which in turn makes a schedulingprocess of base station 100 easier.

In addition, in the present embodiment, as illustrated in FIG. 13,without changing CCE numbers (CCE0 to CCE15) corresponding to the searchspaces for each CC, a correspondence between eREG number as well as RBnumber and CCE number is changed for each CC. However, as illustrated inFIG. 14, without changing the relationship between the CCE number andthe eREG number, the search spaces for the SCell may be configured bycyclically shifting the CCE numbers of CCE in which the search spacesfor the SCell are configured. In other words, in FIG. 13, the CCEsconfigured as the search spaces for each CC are CCE0, CCE5, CCE10, andCCE15 for any one of CCs. In contrast, in FIG. 14, the correspondencebetween eREG number and CCE number of each PRB pair (RB number) does notchange, and the CCE numbers of the CCEs configured as the search spacesfor each CC is different for each CC.

Embodiment 3

In Embodiment 3, a description will be given of a case of switching anoperation of Embodiment 1 (search space configuration in units of PRBpairs) and operation of Embodiment 2 (search space configuration inunits of CCEs). In addition, a base station and a terminal according tothe present embodiment have a basic configuration common to base station100 and terminal 200 according to Embodiment 1, so that the descriptionwill be given with references made to FIGS. 8 and 9.

Specifically, at the time of cross carrier scheduling, configurationsection 102 of base station 100 determines whether a plurality of theePDCCHs having the same aggregation level and the same allocation method(localized allocation or distributed allocation) among the ePDCCHs of aplurality of CCs configured for terminal 200 can be mapped, within onePRB pair of the PCell (without being overlapped). When it is determinedthat the plurality of ePDCCHs can be mapped, configuration section 102applies the operation of Embodiment 2, and when it is determined thatthe plurality of ePDCCHs cannot be mapped, configuration section 102applies the operation of Embodiment 1.

In other words, in a case where the search spaces for the PCell and thesearch spaces for the SCell can be configured in different CCEs (eREGs)within the same PRB pairs, similar to Embodiment 2, configurationsection 102 configures different CCEs within the same PRB pairs among aplurality of PRB pairs included in PDSCH within the PCell, as the searchspaces for the PCell and the search spaces for the SCell.

On the other hand, in a case where the search spaces for the PCell andthe search spaces for the SCell cannot be configured in different CCEs(eREGs) within the same PRB pairs, similar to Embodiment 1,configuration section 102 configures different PRB pairs within the sameRBGs among a plurality of RBGs included in the PDSCH region within thePCell, as the search spaces for the PCell and the search spaces for theSCell.

In other words, configuration section 102 switches a configuration unitof search spaces (allocation unit) between PRB pair (Embodiment 1) andCCE (Embodiment 2) according to the above determination result, andswitches a range (allocation unit group) in which search spaces for eachCC are preferentially configured, between RBG (Embodiment 1) and PRBpair (Embodiment 2).

Here, as an example of conditions of determining whether or not aplurality of the ePDCCHs having the same aggregation level and the sameallocation method can be mapped within one PRB pair, Condition 1(localized allocation) and Condition 2 (distributed allocation) will bedescribed.

Condition 1: whether or not an aggregation level is equal to or lessthan half of a CCE division number per PRB pair in the localizedallocation.

For example, in a case where the CCE division number per PRB pair isfour, if the aggregation level is equal to or less than two (CCEdivision number per PRB pair÷2) (here, aggregation level is one or two),the plurality of ePDCCHs can be mapped within the same PRB pair.Accordingly, configuration section 102 applies the operation ofEmbodiment 2.

On the other hand, in a case where the CCE division number per PRB pairis four, if the aggregation level is equal to or greater than two (CCEdivision number per PRB pair÷2) (here, aggregation level is four), onlyone ePDCCH is mapped in a CCE within the same PRB pair, and theplurality of ePDCCHs cannot be mapped. Accordingly, configurationsection 102 applies the operation of Embodiment 1.

Condition 2: whether or not the number of CCEs configured as the searchspace per PRB pair is equal to or less than a CCE division number perPRB pair in the distributed allocation.

For example, in a case where the CCE division number per PRB pair isfour, if the number of CCEs configured as the search space for theePDCCH per one PRB pair is equal to or less than two (CCE divisionnumber per one PRB pair÷2) in the distributed allocation, a plurality ofthe ePDCCHs can be mapped within the same PRB pair. Accordingly,configuration section 102 applies the operation of Embodiment 2.

On the other hand, when the division number of CCE per PRB pair is four,if the number of CCEs configured as the search space for the ePDCCH perPRB pair is greater than two in distributed allocation, a plurality ofePDCCHs cannot be mapped within the same PRB pair. Accordingly,configuration section 102 applies the operation of Embodiment 1.

In this manner, since configuration section 102 changeably applies thesearch space configuration method depending on Condition 1 or 2,resources to be configured as search spaces vary depending on thecondition.

FIG. 15 illustrates a configuration example of search spaces in a casewhere the operation of Embodiment 1 is applied, and a configurationexample of search spaces in a case where an operation of Embodiment 2 isapplied. In addition, both of the two drawings illustrated in FIG. 15illustrate resources (that is, the same resources) to which signalstransmitted in downlink of the PCell are mapped. For the convenience ofexplanation, FIG. 15 illustrates search spaces for two CCs configuredwithin one CC (the PCell) separately for each of the CCs.

In FIG. 15, it is assumed that a CCE division number per PRB pair isfour and an aggregation level is four. Further, in FIG. 15, with respectto the PCell, search spaces (four CCEs) for a localized allocation areconfigured to RB#1, RB#4, RB#7, and RB#10, respectively, while searchspaces for a distributed allocation are configured to each one eREG(indicated by oblique lines) within RB#1, RB#4, RB#7, and RB#10. Inaddition, CIF number of the SCell is assumed to be 1 (CIF=1).

In other words, in FIG. 15, since the aggregation level (=four) isgreater than two (CCE division number per PRB pair÷2) in localizedallocation, configuration section 102 applies the operation ofEmbodiment 1 with respect to configuring the search spaces for localizedallocation. In other words, configuration section 102 configures the PRBpairs obtained by cyclically shifting the PRB pairs of the PCell withinthe same RBGs as the PRB pairs configured as the search spaces for thePCell, by the value of the CIF number (CIF=1) configured in the SCell,as the search spaces for the SCell.

On the other hand, in FIG. 15, since the number of CCEs configured asthe search space per PRB pair (=one CCE) is equal to or less than aresultant value (CCE division number÷2) in distributed allocation,configuration section 102 applies the operation of Embodiment 2 withrespect to configuring the search space for distributed allocation. Inother words, configuration section 102 configures the eREGs obtained bycyclically shifting the eREGs of the PCell within the same PRB pairs asthe eREGs configured as the search spaces for the PCell, by the value ofthe CIF number (CIF=1) configured in the SCell, as the search spaces forthe SCell.

In this manner, as illustrated in FIG. 15, the search spaces for theSCell of CIF=1 are configured in different RBs, for the localizedallocation and distributed allocation.

In addition, configuration section 205 of terminal 200 performs the sameprocess as the above described configuration section 102 in order toconfigure search spaces.

In this manner, in the present embodiment, base station 100 and terminal200 switch between the operation of Embodiment 1 and the operation ofEmbodiment 2 depending on a condition whether the ePDCCHs of a pluralityof CCs configured for terminal 200 can be mapped in one PRB pair(without being overlapped) in the search space configuration.

Thus, in a case where the ePDCCHs of a plurality of CCs can be mapped inone PRB pair without being overlapped, the search spaces for each CC areconfigured in CCEs (eREGs) different from each other in the same PRBpairs, so that it is possible to reduce the blocking occurrence ratebetween the ePDCCHs having the same aggregation level. In addition, asdescribed in Embodiment 2, the search spaces for a plurality of CCs areconfigured in the same PRB pairs, so that it is possible to allocate thesame antenna port, thereby increasing the transmission power of DMRS.

In addition, in a case where the ePDCCHs of a plurality of CCs cannot bemapped in one PRB pair without being overlapped, the search spaces foreach CC are configured in PRB pairs different from each other in thesame RBG, so that it is possible to reduce the blocking occurrence ratebetween the ePDCCHs having the same aggregation level.

Here, in a case where a plurality of CCs are configured for one terminal200, control signals are transmitted using the same channel. Therefore,it is likely that the ePDCCHs are transmitted while the same aggregationlevel and the same transmission method (allocation method) areconfigured between DL grants or between UL grants. Accordingly, as thepresent embodiment, reducing the blocking occurrence rate between theePDCCHs having the same aggregation level is effective in reducing theblocking rate in the system operation.

Embodiments of the present disclosure have been described thus far.

Other Embodiments

[1] In each of the abovementioned embodiments, a case where the searchspaces for the SCell are configured by using search spaces for the PCellas a reference has been described. However, LTE-Advanced supports crosscarrier scheduling from a certain SCell to another SCell. In this case,instead of parameters relating to the search spaces for the PCell usedas the reference search spaces in the abovementioned embodiments,parameters relating to the search spaces for the SCell corresponding tothe cross carrier scheduling source (CCs in which the search spaces foranother CC are configured) may be used. Alternatively, similar to theabovementioned embodiments, since parameters relating to the PCell areapplied without any change, the same search space configuration processas that of another SCell may be applied even to the SCell of the crosscarrier scheduling source.

[2] In LTE-Advanced, applying different operations respectively to thedownlink and uplink in a base station (also referred to as atransmission point/reception point) to which a terminal is connected hasbeen studied, e.g., assigning downlink data (PDSCH) to the PCell andassigning uplink data (PUSCH) to the SCell. In these operations, it isimportant that, by applying cross carrier scheduling, a UL grant betransmitted from a certain CC (for example, the PCell) to cause uplinkdata to be transmitted from a different CC (for example, the SCell). Byapplying the abovementioned embodiments, it is possible to properlyperform cross carrier scheduling using an ePDCCH even in theseoperations.

[3] The abovementioned embodiments are also applicable to the operationof CoMP (Coordinated Multi Point transmission and reception). CoMP is anoperation to transmit or receive signals simultaneously in a pluralityof base stations, or transmission/reception points (transmission pointsor reception points), or to instantly change the transmission points orthe reception points. In other words, in the operation of CoMP, aplurality of base stations, or the transmission point or reception pointmay be treated like CCs (the PCell and SCell) described in theabovementioned embodiments. More specifically, each of CCs (the PCelland SCell) described in the abovementioned embodiments may be replacedby each base station (or a transmission point or reception point) in theoperation of CoMP, and the same operations as the abovementionedembodiments are applied, thereby allowing search spaces to which acontrol signal intended for each base station is assigned to beconfigured. For example, the PCell in the abovementioned embodiments maybe replaced by a band to be used by a first base station, and the SCellin the above respective embodiments may be replaced by a band to be usedby a second base station different from the first base station. Thus, inthe same frequency (frequency configured in one specific base station ora transmission point or reception point), it is possible to transmit acontrol signal intended for a plurality of base stations or thetransmission points or reception points, in different search spaces. Forexample, in uplink, UL grant may be assigned to a band of a certain basestation (base station having good reception quality. For example,macro-cell), and uplink data (PUSCH) may be assigned to a band of adifferent base station (base station located in the vicinity of aterminal, e.g., pico-cell).

[4] As search spaces for DL grants, the search spaces may be configuredfor each DCI format for downlink to be determined according to atransmission mode. For example, LTE-Advanced requires that two searchspaces be configured per CC for downlink search spaces. Base station 100and terminal 200 may configure search spaces with respect to the twosearch spaces using the same method (for example, a method based on acyclic shift pattern) as the abovementioned embodiments (see FIG. 16).

Note that DCI format 0 (for UL grant) and DCI format 1A (for DL grant)have the same size and can be subjected to blind decoding at the sametime. Therefore, base station 100 may configure a search space for DCIformat 4/DCI format 0/DCI format 1A as a search space for UL grant, andconfigure a search space for a DCI format for DL grant that is dependenton the transmission mode as a search space for DL grant.

In addition, since DCI format 1A is used when communication cannot beperformed using a DCI format with a large number of bits such as a DCIformat for DL that is determined according to the transmission mode andthe like, the usage frequency of DCI format 1A is low. Accordingly, asearch space for DCI format 1A is configured to the same search space asa UL grant (DCI format 0), and there is no significant problem even if aUL grant and a DL assignment cannot be transmitted at the same timeusing the same PRB pair. Furthermore, whether or not DCI format 4 isused varies depending on the transmission mode of the UL, and henceterminal 200 may be configured to perform blind decoding only when DCIformat 4 is used.

As described above, when a predetermined number of search spaces per CCis configured and cross carrier scheduling is also performed, inEquation 1 or Equations 2 and 3, n_(CL) is substituted with n_(CL)*(predetermined number), and thus the same operation as theabovementioned embodiments can be performed. For example, as illustratedin FIG. 16, when base station 100 and terminal 200 configure two searchspaces (search space for DL grant and search space for UL grant) per CCand perform cross carrier scheduling, the same operation can beperformed by substituting n_(CL) with n_(CL)*2 in Equation 1 orEquations 2 and 3. In other words, when a predetermined number (in FIG.16, two) of different search spaces are configured for each format ofcontrol information in each of the PCell and the SCell, base station 100and terminal 200 configure PRB pairs obtained by cyclically shifting PRBpairs configured as the search spaces for the PCell within the same RBG,by the value of the CIF number (in FIG. 16, CIF=1) multiplied by apredetermined number (in FIG. 16, 2=(1*2)), as the search spaces for theSCell.

[5] Although CCEs are described as the division units of PRB pairs inthe abovementioned embodiments, units obtained by further dividing theCCE may be regarded as the division units of PRB pairs, and theabovementioned embodiments may be applied with respect to the divisionunits. For example, units obtained by further dividing the CCE may bedefined as eREGs (or, also simply referred to as “REG”), and theabovementioned embodiments may be applied with respect to the eREGs. Forexample, base station 100 and terminal 200 may configure different eREGswithin the same CCE among a plurality of CCEs included in a PDSCH regionwithin the PCell, as the search spaces for the PCell and the searchspaces for the SCell.

[6] In addition, the value used as the parameter for determining theamount of cyclic shift in the abovementioned embodiments is not limitedto the CIF number, and instead, other identification numbers sharedbetween base station 100 and terminal 200 may be used as the parameter.

[7] The term “antenna port” refers to a logical antenna including one ormore physical antennas. In other words, the term “antenna port” does notnecessarily refer to a single physical antenna, and may sometimes referto an antenna array including a plurality of antennas, and/or the like.

For example, how many physical antennas are included in the antenna portis not defined in LTE, but the antenna port is defined as the minimumunit allowing the base station to transmit different reference signalsin LTE.

In addition, an antenna port may be specified as a minimum unit to bemultiplied by a precoding vector weighting.

[8] In the foregoing embodiments, the present disclosure is configuredwith hardware by way of example, but the disclosure may also be providedby software in cooperation with hardware.

In addition, the functional blocks used in the descriptions of theembodiments are typically implemented as LSI devices, which areintegrated circuits. The functional blocks may be formed as individualchips, or a part or all of the functional blocks may be integrated intoa single chip. The term “LSI” is used herein, but the terms “IC,”“system LSI,” “super LSI” or “ultra LSI” may be used as well dependingon the level of integration.

In addition, the circuit integration is not limited to LSI and may beachieved by dedicated circuitry or a general-purpose processor otherthan an LSI. After fabrication of LSI, a field programmable gate array(FPGA), which is programmable, or a reconfigurable processor whichallows reconfiguration of connections and settings of circuit cells inLSI may be used.

Should a circuit integration technology replacing LSI appear as a resultof advancements in semiconductor technology or other technologiesderived from the technology, the functional blocks could be integratedusing such a technology. Another possibility is the application ofbiotechnology and/or the like.

A transmission apparatus according to this disclosure includes: aconfiguration section that configures, when communication is performedusing a plurality of component carriers (CCs), a first search space anda second search space within a same group of allocation units among aplurality of groups of allocation units included in a data-assignableregion within a first CC, the first search space being a candidate towhich control information for the first CC is assigned, the secondsearch space being a candidate to which control information for a secondCC other than the first CC among the plurality of CCs is assigned; and atransmission section that transmits control information mapped to thefirst search space and control information mapped to the second searchspace.

In the transmission apparatus according to this disclosure, theconfiguration section configures different allocation units within thesame group of allocation units as the first search space and the secondsearch space, respectively.

In the transmission apparatus according to this disclosure: theallocation units are each a physical resource block (PRB) pair, and thegroups of allocation units are each a resource block group (RBG) or asub-band; and the configuration section configures different PRB pairswithin a same RBG or within the same sub-band among a plurality of RBGsas the first search space and the second search space, respectively, theplurality of RBGs being included in the data-assignable region withinthe first CC.

In the transmission apparatus according to this disclosure, theconfiguration section configures, within the same RBG or within the samesub-band where the PRB pairs are referred to as a first PRB pair and asecond PRB pair, the second PRB pair as the second search space, thesecond PRB pair being different from the first PRB pair and beingobtained by cyclically shifting the first PRB pair configured as thefirst search space.

In the transmission apparatus according to this disclosure, a value usedin the cyclic shift is a carrier indication field (CIF) value configuredfor the second CC.

In the transmission apparatus according to this disclosure, when a valueused in the cyclic shift is equal to or greater than a number of PRBpairs forming the RBG, the configuration section configures, as thesecond search space, a third PRB pair within another RBG adjacent to theRBG to which the first PRB pair belongs.

In the transmission apparatus according to this disclosure, theconfiguration section configures, as the second search space, the secondPRB pair obtained by cyclically shifting the first PRB pair within thesame sub-band in preference to the same RBG.

In the transmission apparatus according to this disclosure, when aplurality of precoding resource block groups (PRGs) which are PRBbundling units are included in the same RBG, the configuration sectionpreferentially configures, as the second search space, a PRB pair withina PRG including the first PRB pair among the plurality of PRGs.

In the transmission apparatus according to this disclosure: when anumber of PRB pairs forming the RBG is four, a number of PRB pairsforming the PRG is two; and the configuration section configures one ofthe PRB pairs forming the same PRG, as the first search space, and theother one of the PRB pairs as the second search space.

In the transmission apparatus according to this disclosure: theallocation units are each a control channel element (CCE), and thegroups of allocation units are each a physical resource block (PRB)pair, and the configuration section configures different CCEs within asame PRB pair among a plurality of PRB pairs as the first search spaceand the second search space, respectively, the plurality of PRB pairsbeing included in a data-assignable region within the first CC.

In the transmission apparatus according to this disclosure, theconfiguration section configures, within the same PRB pair where theCCEs are referred to as a first CCE and a second CCE, the second CCE asthe second search space, the second CCE being different from the firstCCE and being obtained by cyclically shifting the first CCE configuredas the first search space.

In the transmission apparatus according to this disclosure, a value usedin the cyclic shift is a carrier indication field (CIF) value configuredfor the second CC.

In the transmission apparatus according to this disclosure, when a valueused in the cyclic shift is equal to or greater than a number of CCEsforming the PRB pair, the configuration section configures, as thesecond search space, a third CCE within another PRB pair adjacent to thePRB pair to which the first CCE belongs.

In the transmission apparatus according to this disclosure, an antennaport allocated to a reference signal for control information to betransmitted in the first search space and an antenna port allocated to areference signal for control information to be transmitted in the secondsearch space are the same.

In the transmission apparatus according to this disclosure, when thefirst search space and the second search space cannot be configured indifferent CCEs, respectively, within the same PRB pair, theconfiguration section sets each of the allocation units to be a physicalresource block (PRB) pair, and each of the groups of allocation units tobe a resource block group (RBG) or a sub-band, and configures differentPRB pairs within a same RBG or within a same sub-band among a pluralityof RBGs as the first search space and the second search space,respectively, the plurality of RBGs being included in a data-assignableregion within the first CC.

In the transmission apparatus according to this disclosure, when anaggregation level in localized allocation is greater than half of anumber of CCEs forming one PRB pair, the configuration sectiondetermines that the first search space and the second search spacecannot be configured in different CCEs, respectively, within the samePRB pair.

In the transmission apparatus according to this disclosure, when anumber of CCEs configured as a search space per PRB pair is greater thanhalf of the number of CCEs forming one PRB pair in distributedallocation, the configuration section determines that the first searchspace and the second search space cannot be configured in differentCCEs, respectively, within the same PRB pair.

In the transmission apparatus according to this disclosure, the first CCis a primary cell and the second CC is a secondary cell.

In the transmission apparatus according to this disclosure, the first CCis a band used by a first base station, and the second CC is a band usedby a second base station different from the first base station.

In the transmission apparatus according to this disclosure, when apredetermined number of different search spaces are configured for eachformat of control information in each of the first CC and the second CC,the configuration section configures, within the same RBG or within thesame sub-band, the second PRB pair as the second search space, thesecond PRB pair being obtained by cyclically shifting the first PRB pairconfigured as the first search space, by a value obtained by multiplyingthe CIF value by the predetermined number.

In the transmission apparatus according to this disclosure, wherein: theallocation units are each a resource element group (REG), and the groupsof allocation units are each a control channel element (CCE); and theconfiguration section configures different REGs within a same CCE amonga plurality of CCEs as the first search space and the second searchspace, respectively, the plurality of CCEs being included in adata-assignable region within the first CC.

A reception apparatus according to this disclosure includes: aconfiguration section that configures, when communication is performedusing a plurality of component carriers (CCs), a first search space anda second search space within a same group of allocation units among aplurality of groups of allocation units included in a data-assignableregion within a first CC, the first search space being a candidate towhich control information for the first CC is assigned, the secondsearch space being a candidate to which control information for a secondCC other than the first CC among the plurality of CCs is assigned; and areception section that receives control information mapped to the firstsearch space and control information mapped to the second search space.

A transmission method according to this disclosure includes:configuring, when communication is performed using a plurality ofcomponent carriers (CCs), a first search space and a second search spacewithin a same group of allocation units among a plurality of groups ofallocation units included in a data-assignable region within a first CC,the first search space being a candidate to which control informationfor the first CC is assigned, the second search space being a candidateto which control information for a second CC other than the first CCamong the plurality of CCs is assigned; and transmitting controlinformation mapped to the first search space and control informationmapped to the second search space.

A reception method according to this disclosure includes: configuring,when communication is performed using a plurality of component carriers(CCs), a first search space and a second search space within a samegroup of allocation units among a plurality of groups of allocationunits included in a data-assignable region within a first CC, the firstsearch space being a candidate to which control information for thefirst CC is assigned, the second search space being a candidate to whichcontrol information for a second CC other than the first CC among theplurality of CCs is assigned; and receiving control information mappedto the first search space and control information mapped to the secondsearch space.

The disclosure of Japanese Patent Application No. 2012-107677, filed onMay 9, 2012, including the specification, drawings and abstract areincorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

The present disclosure is useful in that cross carrier scheduling can beproperly performed in ePDCCHs.

REFERENCE SIGNS LIST

-   -   100 Base station    -   200 Terminal    -   101 Assignment information generation section    -   102, 205 Configuration section    -   103, 207 Error correction coding section    -   104, 208 Modulation section    -   105, 209 Signal assignment section    -   106, 210 Transmission section    -   107, 201 Reception section    -   108, 203 Demodulation section    -   109, 204 Error correction decoding section    -   202 Signal separating section    -   206 Control signal reception section

The invention claimed is:
 1. An integrated circuit which, in operation,controls a process of a communication apparatus, the process comprising:determining a first search space of mapping candidates and a secondsearch space of mapping candidates in a physical resource block set (PRBset) in a data region of a first component carrier, wherein the secondsearch space is configured by shifting control channel elements (CCEs)of the mapping candidates of the first search space by a CarrierIndicator Field value (CIF value) of a second component carrier; anddetecting downlink control information for the first component carrierby decoding the first search space and detecting downlink controlinformation for the second component carrier by decoding the secondsearch space.
 2. The integrated circuit according to claim 1,comprising: circuitry, which, in operation, controls the process; atleast one input coupled to the circuitry, wherein the at least oneinput, in operation, inputs data; and at least one output coupled to thecircuitry, wherein the at least one output, in operation, outputs data.3. The integrated circuit according to claim 1, wherein the PRB setincludes a plurality of CCEs.
 4. The integrated circuit according toclaim 1, wherein each of the mapping candidates of the first searchspace and each of the mapping candidates of the second search space isan Enhanced Physical Downlink Control Channel (EPDCCH) candidate in thedata region.
 5. The integrated circuit according to claim 1, wherein thedata region comprises a plurality of PRB sets and each of the pluralityof PRB sets includes a plurality of CCEs, each CCE including a pluralityof resource element groups (REGs); and a correspondence relationshipbetween CCE numbers and REG numbers in the second search space matches acorrespondence relationship between CCE numbers and REG numbers in thefirst search space.
 6. The integrated circuit according to claim 1,wherein the first search space and the second search space areconfigured in a non-overlapping manner in the PRB set.
 7. The integratedcircuit according to claim 1, wherein the first component carrier is aprimary cell and the second component carrier is a secondary cell.